Expanded tobacco material of this type can be obtained by impregnating a liquid expansion agent into the cellular structure of tobacco material and then rapidly heat-drying the material. In this process, the expansion agent impregnated into the tobacco material is instantly removed from the tobacco material, which expands the tobacco material.
Since this expansion process heats the tobacco material, the tobacco material is exposed to high temperature. As a result, the tobacco material is deteriorated in savor and taste. More specifically, the following fact was confirmed by an analysis of components in tobacco material, which was conducted prior to and after the expansion process. The expansion process reduces duvatrienediol (α-CBT) contained in the tobacco material up to 50 percent or more. The other tobacco components, such as nicotine and saccharide, are also reduced by the expansion process. Duvatrienediol is a kind of leaf lipid-related materials (carbon hydride in an approximate range of C27H56 to C33H68). Duvatrienediol, nicotine and saccharide are flavors inherent in tobacco material.
There has been a well-known apparatus and method for producing a flavor for expanded tobacco material, in which when an expansion agent is impregnated into tobacco material, the tobacco components dissolved in the expansion agent are retrieved from the expansion agent, and fat-soluble ingredients (wax) are removed from the extracted tobacco components in order to compensate a deterioration in savor and taste of the expanded tobacco material (Patent Document 1).
There has been another well-known method (Patent Document 2) in which water-soluble ingredients contained in tobacco components are extracted from tobacco material by causing only the water-soluble ingredients to be absorbed into water. Such water-soluble ingredients are also addible to the expanded tobacco material as flavor.    Patent Document 1: Japanese Patent No. 3014704    Patent Document 2: Japanese Patent No. 3223058